The present disclosure relates to discharge lamps. It finds particular application with regard to high intensity discharge lamps, incandescent lamps, and high energy photovoltaic devices, and the use therein of thermionic or nonthermionic cavity electrodes or coils or combinations thereof. However, it is to be appreciated that the present disclosure will have wide application throughout the lighting and photovoltaic industry.
During operation, as the cathode material in a discharge lamp experiences current and heat in excess of threshold values, i.e., current in the range of 2 to 5 amps and heat in excess of 3200° C., the cathode suffers erosion. This erosion can result in lamp blackening, which decreases lamp efficiency. It is known that the use of a thermionic hollow cathode can help to reduce cathode erosion due to the presence of cavities which increase the surface area of the cathode. In addition, it has been shown that these hollow cathodes can operate at lower current, thus generating less heat. This results in reduced erosion of the cathode material. Cathode surface cavities have been created by use of an etchant deposition process.
However, the hollow cathodes known according to the above technology continue to require high breakdown voltage to ionize the lamp fill gas. One suggested solution to this problem has been the addition of a third electrode. With regard to the use of tungsten cathode material in discharge lamps, it has further been suggested to use a coil structure to reduce the voltage parameter.
Each of the foregoing, while advancing the technology to some degree, fails to fully address the issue of cathode erosion, and particularly tungsten erosion, in discharge lamps, whether mercury or non-mercury based. The invention disclosed herein is intended to provide a cavity structure, which may be applied to one or both of the electrode and/or a coil used in conjunction with the electrode assembly. The inventive cavity structure provides greatly increased surface area in the form of nano-pores, the presence of which enhances lamp performance. As has been stated, ionization of the fill gas in a conventional discharge lamp, or other lamp, requires the application of high voltage, on the average of 2kv. The presence of the nano-pores creates a high electric field, thus reducing the voltage level needed to breakdown the discharge, or fill, gas. The nano-pores created by the subject inventive processing exhibit pore diameters of from about 50 nm to about 500 nm, thus reducing the voltage requirement and the generation of heat to a point that significantly reduces electrode erosion and consequently enhances lamp performance.